The present invention relates to a method for exterminating pests provided with organs for tracheal respiration, such as plant lice, green caterpillars, army worms, etc., which gather on various kinds of plants, such as edible herbs or green or root vegetables, etc. Conventional water culture involves the use of a hydroponic vessel arranged within a spacious cultivation building. The culture solution is put into the hydroponic vessel. The roots of plants are directly immersed in the same culture solution and thereby absorb nutrients. Thus, it becomes unnecessary to use herbicides, soil conditioners, etc. which are used for soil culture. However, many buildings used for water cultivation are open and, therefore, such pests as plant lice, green caterpillars and the like tend to be parasitic on plants. Further, even when the building for cultivation is closed, pests are carried into the building together with seedlings from without.
Thus, there has been, heretofore, used an insecticide or repellent for exterminating such pests. As a result, agricultural chemicals employed remain in the form of residue even in the crop produced by the water culture. Thus, there has arisen a problem to be solved.